High numerical aperture intermediate wide angle objective

ABSTRACT

A 7 group 8 lens photographic objective lens which corrects for aberration.

BACKGROUND OF THE INVENTION

The present invention relates to a high numerical aperture intermediatewide angle lens system of image angle ranging from 55° to 60°, which issmall in size and suitable for use in a single lens reflex camera as aretro focus type objective.

SUMMARY OF THE INVENTION

The present invention involves high numerical aperture intermediate wideangle objective lens system whose aberration is corrected to a highdegree of excellence and which is a retro focus lens system consistingof a 7 group 8 lens system characterized in that the image angle is 55°or greater and which satisfies the following conditions:

    F / 1.4 < |F.sub.1.2 | < F / 0.8 , F.sub.1.2 < 0 1

    F / 1.4 < |F.sub.1.2.3.4 | < F / 0.9     2 ##EQU1##

    1.1 < (ν.sub.1 + ν.sub.2) / (ν.sub.3 + ν.sub.4) < 1.6 4 WHERE;

    F:       is the resultant focal length of the                                          whole optical system;                                                F.sub.1.2...i :                                                                        is the resultant focal length of the first                                    to the i-th lenses;                                                  n.sub.i :                                                                              is the d-line index of refraction of the                                      i-th lens;                                                           ν.sub.i :                                                                           is the Abbe's number of the i-th lens;                               r.sub.k :                                                                              is the radius of curvature of the k-th                                        surface;                                                             d.sub.j :                                                                              is the j-th lens spacing or lens thickness.                      

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the lens system of example 1;

FIG. 2 shows graphs of the aberration curves of example 1;

FIG. 3 shows the lens system of example 2;

FIG. 4 shows graphs of the aberration curves of example 2;

FIG. 5 shows the lens system of example 3; and

FIG. 6 shows graphs of the aberration curves of example 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The first and the second lenses 1 and 2 are of negative meniscus typewhose concave surfaces are directed to the image side; the third and thefourth lenses 3 and 4 are of positive type and are positioned oppositeto the fifth lens with a diaphragm (not shown) positioned therebetween.The fifth lens 5 is of negative type. In example 3 (FIG. 5), the fifthlens 5 and the sixth lens 6 are cemented together. In examples 1 and 2,the sixth lens 6 is of negative type and is cemented to the seventh lens7. In all examples, the seventh and eighth lenses 7 and 8 are ofpositive type. Each example is of 7 group 8 lens structure.

In the conditions indicated below, the characters denote as follows:

    F:       is the resultant focal length of the                                         whole optical system;                                                 F.sub.1.2...i :                                                                       is the resultant focal length of the first                                    to the i-th lenses;                                                   n.sub.i :                                                                             is the d-line index of refraction of the                                      i-th lens;                                                            ν.sub.i :                                                                          is the Abbe's number of the i-th lens;                                r.sub.k :                                                                             is the radius of curvature of the k-th surface;                       d.sub.j :                                                                             is the j-th lens spacing or lens thickness.                       

In accordance with the present invention, the optical system ischaracterized with the following conditions:

    F / 1.4 < |F.sub.1.2 | < F / 0.8 , F.sub.1.2 < 0 1

    F / 1.4 < |F.sub.1.2.3.4 | < F / 0.9     2 ##EQU2##

    1.1 < (ν.sub.1 + ν.sub.2) / (ν.sub.3 + ν.sub.4) < 1.6 4

Condition 1 indicates the power of the front group negative lenses ofthe retro focus lens system. Naturally, for small size, it is necessaryto increase the power of the negative lenses and diminish the spacing.However, if the negative value of the focal length F₁.2 is too muchsmaller than F / 1.4, the desired result is obtained but aberration isaggravated and it is difficult to compensate for aberration at the rearlens group. If focal length F₁.2 is greater than F / 0.8,miniaturization of the lens system is not likely to be attained. Underthis condition, steps must be taken to obtain greater back focus at therear lens group, and also corresponding steps must be taken forcorrection of aberration.

Conditions 2, with relation to the condition 4, indicate steps forcompensation of chromatic aberration, and is, naturally, for correctingaberrations caused under the condition 1. If the focal length F₁.2.3.4is smaller than F / 1.4, the desired chromatic aberration can beadvantageously corrected, but this is apt to cause decrease of Petzvalsum or decrease of the radius of curvature of each surface, andespecially variation of coma aberration. Furthermore, this willdisadvantageously prevent increase in the value of back focus determinedby the focal length F₁.2. On the other hand, a focal length value whichis greater than F / 0.9 is advantageous for Petzval sum, but this willnaturally cause a limitation such that for correction of chromaticaberration, a very small value of Abbe's number ν must be utilized.Thus, condition 2 is most advantageous.

Condition 3 is necessary for miniaturization and also for keepingbalance between the front lens group and the rear lens group. If thevalue of the condition 3 ratio is smaller than the left side value,miniaturization is advantageously attained, but a far greater powercombination is required at the front lens group and this will naturallycause failure of condition 1 and disadvantage in correction. In order toretain vignetting light, in relation to coma aberration, certain stepsare taken such as increasing the diameter of the rear lens group, butthis causes a failure in balance between the front lens group and therear lens group. Further, difficulty is caused in correction ofaberration. This requires such undesirables as increasing the number oflenses used or impossibility in retaining numerical aperture. On theother hand, if condition 3 is greater than 1.3, for the admission of theproper amount of light into the diaphragm aperture, the front lens groupmust be made greater in size. This is contra to the object ofminiaturization and is therefore undesirable.

Condition 4 is closely related with condition 2 and determines the valueof Abbe's number ν which is necessary for correction of chromaticaberration. If (ν₁ + ν₂) / (ν₃ + ν₄) is smaller than 1.1, correction ofchromatic aberration up to the fourth lens is not sufficient andparticularly too much of the transverse chromatic aberration may beproduced. This requires that special steps should be taken at the rearlens group which is undesirable for correction of aberrations. On theother hand, if the last mentioned value of ratio is greater than 1.6, itis feared that correction of chromatic aberration up to the fourth lenswould be too little, and this is undesirable for overall balance ofchromatic aberration.

The data for the examples and the Seidel's coefficients of the examplesare as follows:

    Example 1                                                                     Radius of Curvature                                                                          Lens Spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            92.500       d .sub.1                                                                              3.95   1.51633 / 64.1                              r .sub.2                                                                            57.275       d .sub.2                                                                              9.52                                               r .sub.3                                                                            132.250      d .sub.3                                                                              5.32   1.69350 / 53.3                              r .sub.4                                                                            55.875       d .sub.4                                                                              9.42                                               r .sub.5                                                                            167.500      d .sub.5                                                                              7.50   1.83400 / 37.2                              r .sub.6                                                                            1537.500     d .sub.6                                                                              2.50                                               r .sub.7                                                                            68.313       d .sub.7                                                                              26.50  1.78590 / 44.2                              r .sub.8                                                                            -178.523     d .sub.8                                                                              9.27                                               r .sub.9                                                                            -149.500     d .sub.9                                                                              9.00   1.76182 / 26.6                              r.sub.10                                                                            68.250       d.sub.10                                                                              9.67                                               r.sub.11                                                                            -159.375     d.sub.11                                                                              5.00   1.74077 / 27.8                              r.sub.12                                                                            80.750       d.sub.12                                                                              19.20  1.80610 / 40.8                              r.sub.13                                                                            -79.500      d.sub.13                                                                              3.75                                               r.sub.14                                                                            -951.448     d.sub.14                                                                              8.75   1.78590 / 44.2                              r.sub.15                                                                            -111.275                                                                ______________________________________                                         F = 100.0                                                                     |F.sub.1.2 | = 95.13                                        F.sub.1.2.3.4 = 83.54                                                        Seidel's Coefficients                                                         ______________________________________                                        Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                                0.284    0.131    0.061  0.368  0.198                                 2       -2.375   -0.138   -0.008 -0.595 -0.035                                3       0.493    0.272    0.151  0.310  0.255                                 4       -9.272   -0.324   -0.011 -0.733 -0.026                                5       2.942    0.879    0.263  0.271  0.160                                 6       -0.187   -0.225   -0.270 -0.030 -0.360                                7       4.454    0.977    0.214  0.637  0.187                                 8       3.146    -1.869   1.111  0.247  -0.806                                9       -2.925   1.608    -0.884 -0.289 0.645                                 10      -1.069   -0.892   -0.743 -0.634 -1.148                                11      0.003    -0.010   0.034  -0.267 0.771                                 12      0.264    0.175    0.116  0.026  0.094                                 13      1.593    -0.366   0.084  0.561  -0.148                                14      -0.074   0.120    -0.193 -0.046 0.386                                 15      3.029    -0.261   0.023  0.395  -0.036                                SUM     0.306    0.078    -0.054 0.223  0.134                                 ______________________________________                                    

    Example 2                                                                     Radius of Curvature                                                                          Lens Spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            175.400      d .sub.1                                                                              6.90   1.53172 / 48.9                              r .sub.2                                                                            73.563       d .sub.2                                                                              9.42                                               r .sub.3                                                                            128.468      d .sub.3                                                                              3.00   1.54072 / 47.2                              r .sub.4                                                                            56.023       d .sub.4                                                                              10.95                                              r .sub.5                                                                            168.280      d .sub.5                                                                              15.37  1.83400 / 37.2                              r .sub.6                                                                            -3453.988    d .sub.6                                                                              8.27                                               r .sub.7                                                                            71.325       d .sub.7                                                                              23.82  1.79952 / 42.3                              r .sub.8                                                                            -246.250     d .sub.8                                                                              9.05                                               r .sub.9                                                                            -195.000     d .sub.9                                                                              6.25   1.72825 / 28.5                              r.sub.10                                                                            58.013       d.sub.10                                                                              10.25                                              r.sub.11                                                                            -176.700     d.sub.11                                                                              3.75   1.69895 / 30.1                              r.sub.12                                                                            70.078       d.sub.12                                                                              18.85  1.78590 / 44.2                              r.sub.13                                                                            -79.025      d.sub.13                                                                              0.25                                               r.sub.14                                                                            996.250      d.sub.14                                                                              18.80  1.65830 / 53.4                              r.sub.15                                                                            -155.585                                                                ______________________________________                                         F = 100.0                                                                     |F.sub.1.2 | = 103.37                                       F.sub.1.2.3.4 =76.42                                                         Seidel's Coefficients                                                         Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                                0.042    0.052    0.063  0.198  0.321                                 2       -1.634   -0.162   -0.016 -0.472 -0.049                                3       0.628    0.264    0.111  0.273  0.162                                 4       -7.842   0.147    -0.003 -0.627 0.012                                 5       2.577    0.686    0.183  0.270  0.121                                 6       -0.036   -0.082   -0.186 0.013  -0.393                                7       -3.425   0.878    0.225  0.623  0.217                                 8       3.292    -1.920   1.119  0.181  -0.758                                9       -3.040   1.651    -0.897 -0.216 0.604                                 10      -1.488   -1.040   -0.727 -0.727 -1.016                                11      -0.000   0.000    -0.000 -0.233 0.699                                 12      0.433    0.258    0.154  0.041  0.116                                 13      2.211    -0.480   0.104  0.557  -0.144                                14      -0.063   0.121    -0.233 0.040  0.373                                 15      1.834    -0.388   0.082  0.255  -0.071                                SUM     0.339    -0.015   -0.020 0.177  0.194                                 ______________________________________                                    

    Example 3                                                                     Radius of Curvature                                                                          Lens Spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            217.623      d .sub.1                                                                              6.17   1.49782 / 66.8                              r .sub.2                                                                            69.596       d .sub.2                                                                              9.20                                               r .sub.3                                                                            234.650      d .sub.3                                                                              4.75   1.51454 / 54.7                              r .sub.4                                                                            64.373       d .sub.4                                                                              12.02                                              r .sub.5                                                                            108.900      d .sub.5                                                                              23.57  1.83400 / 37.2                              r .sub.6                                                                            -34888.149   d .sub.6                                                                              6.52                                               r .sub.7                                                                            91.838       d .sub.7                                                                              21.75  1.78800 / 47.5                              r .sub.8                                                                            -269.731     d .sub.8                                                                              12.27                                              r .sub.9                                                                            -215.345     d .sub.9                                                                              5.00   1.84666 / 23.9                              r.sub.10                                                                            57.528       d.sub.10                                                                              9.77   1.78800 / 47.5                              r.sub.11                                                                            79.998       d.sub.11                                                                              13.67                                              r.sub.12                                                                            -87.823      d.sub.12                                                                              10.60  1.77250 / 49.6                              r.sub.13                                                                            -62.057      d.sub.13                                                                              0.25                                               r.sub.14                                                                            182.638      d.sub.14                                                                              14.45  1.81600 / 46.8                              r.sub.15                                                                            -229.152                                                                ______________________________________                                         F = 100.0                                                                     |F.sub.1.2 | = 92.05                                        F.sub.1.2.3.4 = 85.04                                                        Seidel's Coefficients                                                         Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                        1       0.022    0.047    0.102  0.153  0.554                                 2       -2.087   -1.194   -0.683 -0.478 -0.664                                3       0.324    0.383    0.452  0.145  0.705                                 4       -7.452   -3.837   -1.976 -0.528 -1.289                                5       5.660    3.694    2.411  0.418  1.846                                 6       -0.005   -0.025   -0.125 0.001  -0.612                                7       1.232    1.165    1.102  0.480  1.496                                 8       2.528    -0.212   0.018  0.163  -0.015                                9       -2.383   0.094    -0.004 -0.213 0.009                                 10      -0.066   -0.074   -0.082 -0.031 -0.126                                11      -0.630   -0.970   -1.496 -0.551 -3.155                                12      -0.093   0.035    -0.014 -0.496 0.194                                 13      1.778    0.654    0.240  0.702  0.346                                 14      -0.002   -0.010   -0.041 0.246  0.853                                 15      1.473    0.372    0.094  0.196  0.073                                 SUM     0.299    0.122    -0.000 0.208  0.217                                 ______________________________________                                    

In the foregoing examples, the number of the lens surfaces and theradius of curvature are taken from the left hand side of the figures.

What is claimed is:
 1. An intermediate wide angle retro focus objectivelens system comprising a 7 group, 8 element lens wherein the lenselements have the following characteristics:

    Radius of Curvature                                                                          Lens spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            92.500       d .sub.1                                                                              3.95   1.51633 / 64.1                              r .sub.2                                                                            57.275       d .sub.2                                                                              9.52                                               r .sub.3                                                                            132.250      d .sub.3                                                                              5.32   1.69350 / 53.3                              r .sub.4                                                                            55.875       d .sub.4                                                                              9.42                                               r .sub.5                                                                            167.500      d .sub.5                                                                              7.50   1.83400 / 37.2                              r .sub.6                                                                            1537.500     d .sub.6                                                                              2.50                                               r .sub.7                                                                            68.313       d .sub.7                                                                              26.50  1.78590 / 44.2                              r .sub.8                                                                            -178.523     d .sub.8                                                                              9.27                                               r .sub.9                                                                            -149.500     d .sub.9                                                                              9.00   1.76182 / 26.6                              r.sub.10                                                                            68.250       d.sub.10                                                                              9.67                                               r.sub.11                                                                            -159.375     d.sub.11                                                                              5.00   1.74077 / 27.8                              r.sub.12                                                                            80.750       d.sub.12                                                                              19.20  1.806610 / 40.8                             r.sub.13                                                                            -79.500      d.sub.13                                                                              3.75                                               r.sub.14                                                                            -951.448     d.sub.14                                                                              8.75   1.78590 / 44.2                              r.sub.15                                                                            -111.275                                                                ______________________________________                                         F = 100.0                                                                     |F.sub.1.2 | = 95.13                                        F.sub.1.2.3.4 = 83.54.                                                       Seidel's Coefficients                                                         Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                        1       0.284    0.131    0.061  0.368  0.198                                 2       -2.375   -0.138   -0.008 -0.595 -0.035                                3       0.493    0.272    0.151  0.310  0.255                                 4       -9.272   -0.324   -0.011 -0.733 -0.026                                5       2.942    0.879    0.263  0.271  0.160                                 6       -0.187   -0.225   -0.270 -0.030 -0.360                                7       4.454    0.977    0.214  0.637  0.187                                 8       3.146    -1.869   1.111  0.247  -0.806                                9       -2.925   1.608    -0.884 -0.289 0.645                                 10      -1.069   -0.892   -0.743 -0.634 -1.148                                11      0.003    -0.010   0.034  -0.267 0.771                                 12      0.264    0.175    0.116  0.026  0.094                                 13      1.593    -0.366   0.084  0.561  -0.148                                14      -0.074   0.120    -0.193 -0.046 0.386                                 15      3.029    -0.261   0.023  0.395  -0.036                                SUM     0.306    0.078    -0.054 0.223  0.134                                 ______________________________________                                    

Wherein the lenses are numbered from 1 to 8 from the object side, andlenses 5 and 6 form doublets; and wherein

    F:     is the resultant focal length of the whole                                    optical system;                                                        F.sub.1.2...i :                                                                      is the resultant focal length of the first to the                             i-th lenses;                                                           n.sub.i :                                                                            is the d-line index of refraction of the i-th                                 lens;                                                                  ν.sub.i :                                                                         is the Abbe's number of the i-th lens;                                 r.sub.k :                                                                            is the radius of curvature of the k-th                                        surface; and                                                           d.sub.j :                                                                            is the j-th lens spacing or lens thickness.                        


2. An intermediate wide angle retro focus objective lens systemcomprising a 7 group, 8 element lens wherein the lens elements have thefollowing characteristics:

    Radius of Curvature                                                                          Lens Spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            175.400      d .sub.1                                                                              6.90   1.53172 / 48.9                              r .sub.2                                                                            73.563       d .sub.2                                                                              9.42                                               r .sub.3                                                                            128.468      d .sub.3                                                                              3.00   1.54072 / 47.2                              r .sub.4                                                                            56.023       d .sub.4                                                                              10.95                                              r .sub.5                                                                            168.280      d .sub.5                                                                              15.37  1.83400 / 37.2                              r .sub.6                                                                            -3453.988    d .sub.6                                                                              8.27                                               r .sub.7                                                                            71.325       d .sub.7                                                                              23.82  1.79952 / 42.3                              r .sub.8                                                                            -246.250     d .sub.8                                                                              9.05                                               r .sub.9                                                                            -195.000     d .sub.9                                                                              6.25   1.72825 / 28.5                              r.sub.10                                                                            58.013       d.sub.10                                                                              10.25                                              r.sub.11                                                                            -176.700     d.sub.11                                                                              3.75   1.69895 / 30.1                              r.sub.12                                                                            70.078       d.sub.12                                                                              18.85  1.78590 / 44.2                              r.sub.13                                                                            -79.025      d.sub.13                                                                              0.25                                               r.sub.14                                                                            996.250      d.sub.14                                                                              18.80  1.65830 / 53.4                              r.sub.15                                                                            -155.585                                                                ______________________________________                                         F = 100.0                                                                     |F.sub.1.2 | = 103.37                                       F.sub.1.2.3.4 = 76.42.                                                       Seidel'3 Coefficients                                                         Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                        1       0.042    0.052    0.063  0.198  0.321                                 2       -1.634   -0.162   -0.016 -0.472 -0.049                                3       0.628    0.264    0.111  0.273  0.162                                 4       -7.842   0.147    -0.003 -0.627 0.012                                 5       2.577    0.686    0.183  0.270  0.121                                 6       -0.036   -0.082   -0.186 0.013  -0.393                                7       -3.425   0.878    0.225  0.623  0.217                                 8       3.292    -1.920   1.119  0.181  -0.758                                9       -3.040   1.651    -0.897 -0.216 0.604                                 10      -1.488   -1.040   -0.727 -0.727 -1.016                                11      -0.000   0.000    -0.000 -0.233 0.699                                 12      0.433    0.258    0.154  0.041  0.116                                 13      2.211    -0.480   0.104  0.557  -0.144                                14      -0.063   0.121    -0.233 0.040  0.373                                 15      1.834    -0.388   0.082  0.255  -0.071                                SUM     0.339    -0.015   -0.020 0.177  0.194                                 ______________________________________                                    

Wherein the lenses are numbered from 1 to 8 from object side, and lenses6 and 7 form doublets; and wherein

    F:        is the resultant focal length of the whole                                    optical system;                                                     F.sub.1.2....i :                                                                        is the resultant focal length of the first                                    to the i-th lenses;                                                 n.sub.i : is the d-line index of refraction of the                                      i-th lens;                                                          ν.sub.i :                                                                            is the Abbe's number of the i-th lens;                              r.sub.k : is the radius of curvature of the k-th                                        surface; and                                                        d.sub.j : is the j-th lens spacing or lens thickness.                     


3. An intermediate wide angle retro focus objective lens systemcomprising a 7 group, 8 element lens wherein the lens elements have thefollowing characteristics:

    Radius of Curvature                                                                          Lens Spacing                                                   in m m         in m m       n.sub.i / ν.sub.i                              ______________________________________                                        r .sub.1                                                                            217.623      d .sub.1                                                                              6.17   1.49782 / 66.8                              r .sub.2                                                                            69.596       d .sub.2                                                                              9.20                                               r .sub.3                                                                            234.650      d .sub.3                                                                              4.75   1.51454 / 54.7                              r .sub.4                                                                            64.373       d .sub.4                                                                              12.02                                              r .sub.5                                                                            108.900      d .sub.5                                                                              23.57  1.83400 / 37.2                              r .sub.6                                                                            -34888.149   d .sub.6                                                                              6.52                                               r .sub.7                                                                            91.838       d .sub.7                                                                              21.75  1.78800 / 47.5                              r .sub.8                                                                            -269.731     d .sub.8                                                                              12.27                                              r .sub.9                                                                            -215.345     d .sub.9                                                                              5.00   1.84666 / 23.9                              r.sub.10                                                                            57.528       d.sub.10                                                                              9.77   1.78800 / 47.5                              r.sub.11                                                                            79.998       d.sub.11                                                                              13.67                                              r.sub.12                                                                            -87.823      d.sub.12                                                                              10.60  1.77250 / 49.6                              r.sub.13                                                                            -62.057      d.sub.13                                                                              0.25                                               r.sub.14                                                                            182.638      d.sub.14                                                                              14.45  1.81600 / 46.8                              r.sub.15                                                                            -229.152                                                                ______________________________________                                         F = 100.0?                                                                    |F.sub.1.2 | = 92.05?                                       F.sub.1.2.3.4 = 85.04.                                                       Seidel's Coefficients                                                         Lens                                                                          Surface S.sub.1  S.sub.2  S.sub.3                                                                              S.sub.4                                                                              S.sub.5                               ______________________________________                                        1       0.022    0.047    0.102  0.153  0.554                                 2       -2.087   -1.194   -0.683 -0.478 -0.664                                3       0.324    0.383    0.452  0.145  0.705                                 4       -7.452   -3.837   -1.976 -0.528 -1.289                                5       5.660    3.694    2.411  0.418  1.846                                 6       -0.005   -0.025   -0.125 0.001  -0.612                                7       1.232    1.165    1.102  0.480  1.496                                 8       2.528    -0.212   0.018  0.163  -0.015                                9       -2.383   0.094    -0.004 -0.213 0.009                                 10      -0.066   -0.074   -0.082 -0.031 -0.126                                11      -0.630   -0.970   -1.496 -0.551 -3.155                                12      -0.093   0.035    -0.014 -0.496 0.194                                 13      1.778    0.654    0.240  0.702  0.346                                 14      -0.002   -0.010   0.041  0.246  0.853                                 15      1.473    0.372    0.094  0.196  0.073                                 SUM     0.299    0.122    -0.000 0.208  0.217                                 ______________________________________                                    

Wherein the lenses are numbered from 1 to 8 from the object side, andlenses 6 and 7 form doublets; and wherein

    F:       is the resultant focal length of the whole                                    optical system;                                                      F.sub.1.2....i :                                                                       is the resultant focal length of the first                                    to the i-th lenses;                                                  n.sub.i :                                                                              is the d-line index of refraction of the i-th                                 lens;                                                                ν.sub.i :                                                                           is the Abbe's number of the i-th lens;                               r.sub.k :                                                                              is the radius of curvature of the k-th                                        surface; and                                                         d.sub.j :                                                                              is the j-th lens spacing or lens thickness.                      